The present invention relates to an ultrasound imaging device having a beamformer that makes it possible to perform high-definition scanning.
In conventional medical ultrasound imaging systems, there are speckles formed from ensembles of fine scatterers which are smaller than the wave resolution of the systems in principle. In common B-mode imaging in which an attempt is made to recognize in vivo information by locating very small reflection intensity changes, luminance changes in relevant speckle signals are often nearly equivalent to that of reflection intensity changes useful for in vivo diagnosis. It is well-known problem that this equivalence makes it difficult to recognize the in vivo information.
There are several known methods which address the above problem. One method beamforms transmit and receive beam signals at multiple probe aperture positions and/or multiple imaging frequencies, and then adds the signals as coherent signals reserving carrier phase information. Another method provides a wave detection process after beamforming, and then adds the beamformed signals as incoherent signals from which the carrier phase information has been removed. The former method, which performs addition with coherent signals, is expected to reduce the size of the speckle by improving the diffraction limit of the transmission/reception aperture and increasing the frequency bandwidth. The latter method is widely known as so-called compound techniques. The compound techniques can be categorized into two types: “spatial compound technique” and “frequency compound technique.” The “spatial compound technique” compounds signals from multiple probe aperture positions, whereas the “frequency compound technique” compounds multiple frequency band signals. As regards the “spatial compound technique,” which compounds transmission/reception results obtained from multiple directions, the quality of a compounded image depends on a problem of blurring to be solved when the beams are compounded, which may be caused, for instance, by probe movement or improper sound velocity assumption. A relevant correction technology is disclosed, for instance, in JP-T No. 2002-526225.